1. Field of the Invention
The invention relates to a method for creating charged-particle-beam exposure data containing a description of an exposure sequence of character patterns when performing exposure of a charged particle beam according to a character projection technique; a program for creating exposure data; and a method for manufacturing a semiconductor device that uses the created exposure data.
2. Description of the Related Art
When writing device circuit patterns on resists over semiconductor substrates, electron beam lithography technology, particularly an electron-beam direct writing technique, does not require creation of masks, which are used as original patterns of circuit patterns, every devices. As such, the technology is used for prototype development and research/development in regard to cost reduction and QTAT (quick turn around time).
According to the electron beam lithography, a circuit pattern to be transferred is segmented into basic unititary patterns. Then, electron beams having the same shapes and sizes as those of the each unit pattern shaped using shaping aperture masks, and are then sequentially radiated over resists. Such a irradiation of the electron beam is alternatively expressed using the term “shot.”
Techniques for shaping electron beams have two types. They are a variable shaped beam (VSB) technique and a character projection (CP) technique. In the VSB technique, a rectangular beam, which is shaped into a rectangular through a first shaping aperture mask, is partly applied to a rectangular aperture of a second shaping aperture mask, and a rectangular beam of an arbitrarily size is thereby created. In the CP technique, a rectangular beam shaped through a first shaping aperture mask is applied to an arbitrarily shaped aperture opened through a second shaping aperture mask, and a beam having the same shape as the aperture is thereby created. The aperture whose shape itself is a character shape is referred to as a “character aperture.”
A second shaping aperture mask of the above-described type that has a plurality of character apertures and a VSB exposure rectangular aperture is referred to as a “character aperture mask” or “CP aperture mask.” In addition, a “shaping deflector” refers to a deflector that deflects an electron beam shaped through the first shaping aperture mask. An electron beam is thus deflected using the shaping deflector, the electron beam is then applied to an arbitrarily or rectangular aperture of the CP aperture mask, and the electron beam is thereby shaped.
The electron beam shaped through the CP aperture is applied through an objective reflector composed of at least two main and sub deflectors onto specified positions of a semiconductor substrate that is to be exposed. Ordinarily, irradiation positions of the shaped electron beam to specimens are determined to be deflection regions divided corresponding to the main and sub deflectors. The main deflector is capable of deflecting a region larger than a region deflectable with the sub deflector; and the sub deflector is capable of deflecting a small region at a high speed.
The main deflector, sub deflector, and shaping deflector determines irradiation positions of electron beam onto the specimen and position of the character aperture for creating the shaped beam in the shape of the character pattern to be transferred. Voltage or current is applied to each of these deflectors via an amplifier for individual deflectors to attain a desired deflection amount. Specifically, voltage is applied to the deflector of an electrostatic type (electrostatic deflector), and current is applied to the deflector of an electromagnetic type (electromagnetic deflector).
Herein below, a case where electrostatic deflectors are used will be described referring to FIGS. 18A and 18B. Shown in the figures is the relationship between a settling time and a deflection distance in the case of deflection by the electrostatic deflector. As shown in FIG. 18A, it takes a time before a desired deflection region enters a setting state after application of voltage. Assume that an electron beam is desired to deflect by Lx and Ly in an x direction and a y direction in a sub deflection region. In this case, when an electron beam is applied with a shot after a time t1 has elapsed, the electron beam can be positioned in a precise manner from a present position P0 to a desired position P1 to write a pattern, as shown in FIG. 18B. However, when the electron beam is applied with a shot after a time t2 (t2<t1) shown in FIG. 18A has elapsed, the pattern is wrote at a position P2, which deviates from the position P1. This example corresponds to the following cases. One case is that, for example, when the shaping deflector is used; the beam is off from a character aperture that is to be selected. Another case is that, for example, when a rectangular beam is shaped using the VSB technique, the size of the shaped beam is varied. Another case is that when the main deflector is used, the position of a sub deflection region to be selected deviates, whereby patterns to be transferred with a shot before the beam reaches a setting level are caused to individually deviate from desired positions corresponding to the deviation in the position of the sub deflection region.
To prevent the problems described above, conventional electron-beam exposure apparatuses are designed as described hereunder. Like the time t1 shown in FIG. 18A, settling times are set as necessary for use as settling times for individual deflectors. More specifically, the settling times are set in units of each shot (for a sub deflector), in units of each selection of a sub deflection region (for a main deflector), and in units of each change in the shape of a character beam or a variable shaping beam (VSB) (for a shaping deflector).
The settling time (t1) necessary for each of the deflectors to deflect an electron beam increases and decreases depending on the deflection distance. As such, an electron-beam exposure apparatus has been proposed in which the settling time is set variably depending on the deflection length. In this case, since the sum of the settling times can be reduced, the throughput can be enhanced in comparison to a case where only fixed settling times are set.
In this case, however, a problem is held pending resolution in the shot sequence of character patterns. If the shot sequence of character patterns in sub deflection regions can be appropriately determined, the sum of deflection amounts of the sub deflectors can be reduced, and the total exposure time can be reduced, accordingly.